Quantifying Injection-Driven Interphase Mass Transfer within Porous Media via Time-Elapsed X-ray micro-Computed Tomography

Abstract

Understanding interphase mass transfer is essential for a variety of applications in porous media, ranging from groundwater remediation to geologic energy storage. While X-ray micro-Computed Tomography ($\mu$CT) provides critical \textit{in situ} observations, its application in quantifying mass transfer phenomena requires models and workflows compatible with spatial and temporal constraints. Current literature presents three analytical frameworks for evaluating interphase mass transfer using time-lapsed sequences of $\mu$CT scans: the Slice-Averaged Concentration (SAC) approach, the Non-Classified per-Cluster (NPC) approach, and the Classified per-Cluster (CPC) approach. Comparing results with previous studies, we identify that further research is needed to understand how these approaches will vary with experimental conditions and how the physical implications of their calculation frameworks should affect the interpretation of the results, as there are often no ground-truth measurements to compare the estimates to. The current study systematically evaluates the frameworks and results of the three approaches as applied to several sequences of time-lapsed $\mu$CT scans, each observing hydrogen dissolution experiments at varying injection rates. For each observed advective injection rate, results indicate that system-scale properties, like mass transfer, appear robust to the selected approach. However, approach estimates diverged when approximating more complex, pore-scale phenomena, such as aqueous solute concentration. Ultimately, the utility of one approach over another is determined by the desired level of system detail, at the cost of the computational resources required to achieve it. Our results provide a framework for researchers to select analytical approaches based on available computational resources and the desired level of physical detail.